US 2010/0283560 discloses a device for use in explosion-risk areas, in which two appliances can be connected to one another without any problems via a transmission line, for data interchange purposes, by providing decoupling networks on the input side of the appliances, which are dimensioned and designed such that the energy which can be stored in the decoupling network cannot exceed a predeterminable maximum value. This is intended to effectively prevent the creation of ignition sparks, which could lead to an explosion of a gas mixture in explosion-risk areas, while complying with the respectively applicable explosion protection standards. The network interface is also intended to comply with the Ethernet transmission standard. The transmission element in DE 10 2007 036 964 A1 builds on a standard Ethernet circuit, in which the transmission elements for the decoupling network are formed with capacitors, in order to limit the energy which can be stored in the transmission elements.
DE 10 2005 042 257 B4 discloses data communication being provided in the explosion-risk mining field on the one hand via wireless LAN (WLAN) and on the other hand by commercially available standard components, in which case the electrical Ethernet data communication which is used internally in the appliances is converted via medium converters to optical signals, in order then to use these optical signals in the network infrastructure of the mine. The standard components are encapsulated, potted, in an intrinsically safe form in the central unit, and are accommodated in a housing, which is licensed as being intrinsically safe, and is composed, in particular, of stainless steel.
In the meantime, the demand for automation in explosion-risk areas, for example in coal mining, have become as great as those above ground. In general, centrally arranged control stations are used for machine control and monitoring of mobile machines which are used in hazardous areas, and are positioned in those areas in which there are no problems with explosion protection. In order to allow above-ground control stations, for example, to also control and monitor complex automation processes, a large number of different sensors and actuators, including measurement and diagnosis systems, are required, although these have to be used in the explosion-risk area. Even in explosion-risk areas, there are therefore demands to allow an interface network which has become established in normal areas of application, in particular a network based on the Ethernet protocol, to be used. Ethernet based on the use of glass fibres is nowadays used predominantly in explosion-risk areas. The maintenance and servicing effort is considerably greater here. The glass fibre cable does not offer the capability to provide an electrical supply to the communication subscriber.